Scatter graphics: League 2, 2021-22

Now that the season is over (barring play-offs which I exclude for consistency), I can create final versions of the scatter graphics. These compare the attacking and defensive performances of every team in a division – each of the four graphics is explained briefly below and at length here.

Shot dominance

First of all, here is how the number of shots taken by each club compares with those they face in return. The average number of shots taken per match is on the horizontal and the average number faced is on the vertical, so bottom right (take plenty, allow few in return) is good while top left (take few, allow plenty) is bad. The stripes are like contours: the greener the stripe, the better the performance (and vice versa for red).

Unfortunately Scunthorpe‘s relegation was no surprise: their shot difference was the worst in the division by a wide margin. Newport and Bradford both had attacks worthy of a promotion push but were let down by their openness at the back.

Attacking effectiveness

Now let’s look at attacking alone. The horizontal axis stays the same as in the graphic above, but now the vertical shows the average number of shots needed to score each league goal. Therefore bottom right is good (taking lots of shots and needing fewer efforts to convert) and top left is bad:

Carlisle‘s woes this season can be partly explained by their wastefulness in front of goal: despite creating a respectable number of chances they needed more attempts to find the net on average than everyone except bottom side Scunthorpe. Meanwhile Port Vale secured a play-off finish thanks to the division’s most ruthless finishing rather than an especially productive attack – they only just out-shot relegated Oldham.

Defensive effectiveness

Next let’s look at the defensive situation – basically take the above chart and replace the word “taken” for “faced” on both axes. Now top left is good – facing fewer shots and able to soak up more per goal conceded – and bottom right is bad:

Tranmere almost defended their way to the play-offs this season, soaking up over four more chances per goal conceded than the average team. Harrogate allowed a similar number of chances – and had a respectable shot difference overall – but found themselves in the bottom half of the table after conceding almost twice as readily.

Expected goals

Finally here’s an attempt at correcting the first graphic for the quality of chances created and allowed, using the same “expected goals” values that power my shot timelines (explained here). The reason for doing this is that the results tend to correlate more strongly with performance than when we treat all shots equally:

When we adjust for shot quality the worst two teams are the ones who went down, while the top two of Forest Green and Exeter lead a congested field. Bristol Rovers sealed automatic promotion despite some fairly modest underlying performances, so perhaps they were doing something interesting that the data didn’t pick up.